German published patent application DE 3,832,185 Al discloses a moisture sensor which utilizes the moisture-dependent refractive index change of a boundary layer in an interferometer. The moisture-sensitive layer is arranged between porous reflectors.
U.S. Pat. No. 4,712,865 discloses the utilization of polysiloxanes in fiber-optic gas sensors; however, information as to the configuration of a sensor is not provided.
Integrated optical Mach-Zehnder interferometers are disclosed in the paper by Ludwig Ross entitled "Integrated Optical Components in Substrate Glasses", published in "Glastechnische Berichte" Volume 62 (1989), Number 8, pages 285 to 297.
The use of Mach-Zehnder interferometers is disclosed in the article of J. Dakin et al entitled "Optical Fiber Sensors; Principles and Components", published by Artech House, Boston, London 1987 without a superstrate layer defining a hydrogen sensor.